An electronic camera often adopts a low-cost, high-precision contrast detection (scan AF) autofocusing apparatus which adjusts the focus in accordance with the high-frequency component of the image signal of an object image formed on an image sensing element while driving a focus lens. However, it becomes difficult for such an electronic camera to realize both a high AF precision and high speed along with increases in magnification and the number of pixels. To meet this demand, there has been proposed a system which comprises an external distance measurement device of a passive type or the like and measures the distance by switching between distance measurement and contrast detection or performing the two operations.
A conventional technique of performing distance measurement by switching between distance measurement and contrast detection or performing the two operations is disclosed in, e.g., Japanese Patent Laid-Open Nos. 5-119250, 2000-111792, and 2003-107333.
Japanese Patent Laid-Open No. 5-119250 discloses the following technique.
Both autofocusing using contrast detection and autofocusing using infrared detection are employed. In normal photographing operation, the focus is adjusted by an autofocusing apparatus using contrast detection. In only a photographing environment in which it becomes difficult to execute focusing operation by the autofocusing apparatus using contrast detection, the autofocusing apparatus is switched to an autofocusing means using infrared detection, and distance measurement operation and autofocusing operation are done for a desired object. This technique can realize proper autofocusing regardless of the brightness of the object.
Japanese Patent Laid-Open No. 2000-111792 discloses the following technique.
This technique employs both an autofocusing means using contrast detection of photoelectrically converting an object image to generate an image signal, detecting a predetermined high-frequency component from the generated image signal, and adjusting the focus, and an autofocusing means using infrared detection of receiving light reflected by an object from a light-emitting means (LED) which emits infrared rays, and detecting an output signal corresponding to the object distance. Autofocusing operation is performed by selecting either the autofocusing means using contrast detection or the autofocusing means using infrared detection in accordance with an output from a temperature detection means for detecting the ambient temperature. This technique can execute appropriate autofocusing regardless of a change in the temperature of the use environment.
Japanese Patent Laid-Open No. 2003-107333 discloses the following technique.
The purpose of this reference is “to provide an autofocusing apparatus and method excellent in both the response characteristic and precision”. The solving means is “an autofocusing apparatus for an image sensing element, comprising distance measurement means for detecting a distance to an object, lens driving means for driving a photographing lens of an image sensing apparatus, focus detection means for detecting a focus of the object by using an image sensor of the image sensing apparatus, correction means for correcting the lens driving means in accordance with a focus detection result of the focus detection means, and determination means for determining effectiveness of the correction means”.
However, in Japanese Patent Laid-Open No. 5-119250, autofocusing operation is done by the autofocusing means using contrast detection in normal photographing operation, and thus the autofocusing speed cannot be increased in normal photographing operation. When the autofocusing means is switched to one using infrared detection in only a photographing environment in which it becomes difficult to execute autofocusing operation by the autofocusing apparatus using contrast detection, a satisfactory precision of autofocusing operation cannot be obtained.
In Japanese Patent Laid-Open No. 2000-111792, either the autofocusing means using contrast detection or the autofocusing means using infrared detection is selected in accordance with a change in the temperature of the use environment. This technique also suffers the same problems as those of Japanese Patent Laid-Open No. 5-119250.
Japanese Patent Laid-Open No. 2003-107333 discloses the technique which corrects the lens driving means in accordance with the focus detection result of the focus detection means and employs the determination means for determining effectiveness of the correction. However, this reference does not provide any solution to noncoincidence between the detection regions of the distance measurement means and focus detection means that is caused b parallax, and any solution to unbalance between the detection precisions of the distance measurement means and focus detection means.